The most notable changes in man-pages-3.73 are various new and modified pages describing namespaces in general, and user and PID namespaces in detail:

A new namespaces(7) page provides an overview of Linux namespaces. Linux currently supports six namespaces (IPC, mount, network, PID, UTS, and user), and each namespace wraps some global system resource(s) in an abstraction that makes it appear to the processes within the namespace that they have their own isolated instance of the resource(s). Much of the content this and the other new pages in this release was drawn from a series of articles that I wrote for LWN.net in January 2013, but a few details have changed since and are documented the new man pages.